After playing through a bit, stuck about midway in Mine1 at around 200 deaths and the comments I have are kinda as followed:
I think the controls feel super crisp for the most part, but I do think if you have the expectation of gun shots to happen mid air during a spindash off a cliff, the bullets should fly out upon button press, not spin finish. A lot of times it just feels bad. Like, I don't mind the platforming challenge, that actually feels good for the most part (I do like the MMX1-3 Dash Jump speed boosting), but the DKC spin off a cliff mechanic combined with shooting genuinely feels bad at times, and I don't feel like I'm in control of my precision as a result.
Some enemies are also annoying because they feel very inconsistent. The game does not do a good job of indicating "this will damage you, don't touch" and "this can be destroyed, but this cannot." This is usually not a problem if two objects are distinctly different (I.E. Sawblades clearly painful, but rabbits are not), but walking penguin can be destroyed while pickaxe penguin bullets go through. It's not a good indicator system, and becomes more frustrating than interesting.
If you want to make a precision platformer, which reading your responses makes me feel like you wanted that more than something as boiled down as "insanely difficult," I'd look back on games like Super Meat Boy, which does a very good job of showing you a path without showing you how. You aren't making a Kaizo game as far as I can tell, so you should capitalize on rewarding the bold, but that demands controls that allow you to feel in completely in control. You want to feel like the game is against you, not inputs.
As I said earlier, the actual movement feels SUPER clean, with the MMX-styled dash jumping feeling really good, but if you include a mechanic for mid-air precision, it should feel just as good. If you aren't making a Kaizo, there should be clear indicators on how something is approached, I.E. adding a slight red tinge to something that can be damaged vs a soft blue shade if its neutral.
I'll likely come back to this to try again, but those are my thoughts currently, otherwise I do think you should reconsider your difficulty rating system in the game, or emphasize this is a precision platformer, as I think that better fits the goal I'm getting out of this.